Check 21, became effective on October 28, 2004. Check 21, allows checks to clear more quickly due to increased efficiency through the use of electronic image technology. Original checks will be copied, sent electronically to the clearing institution and the substitute check will be cleared. Check 21, does not affect the way that you write checks or accept checks. The time it takes for a check to clear can decrease dramatically. In the past, it could take days for checks to clear an account. But with Check 21, it could take just hours for a check to clear.